Pasty multi-component masses, such as dental impression masses, are produced by means of mixing devices in which the individual components of the mass are simultaneously supplied from separate cartridge cylinders to a mixer which dispenses the mixed paste from a front end. The mixer may be a static mixer or a dynamic mixer (having a rotary mixer element). The paste exiting from the front end of the mixer may be supplied directly onto an impression spoon.
Depending on the viscosity and mixing ratio, the fact that the pressure builds up differently in the individual cartridge cylinders at the start of the device may cause the components to reach the mixer at different times. In such a case, the first length of paste exiting from the mixer has a mixing ratio which differs from a desired value and may therefore cure less perfectly or more slowly, or have other undesired properties.
In case one of the components is a base paste and the other is a catalyst of a dental impression mass, a typical mixing ratio of base paste to catalyst is 5:1. Due to the different properties and/or amounts of material and the differently sized inlet openings of the mixer, it can be observed that the mixing chamber is filled with the base paste before the catalyst arrives, so that a first length of approximately 3 cm of the final paste fails to have the desired mixing ratio.
Known is a static mixer for producing pastes from different amounts of components, which includes a housing having at its rear end an inlet opening for each component. A space provided between a mixing chamber and a plate, which has the inlet openings for the two components, is divided into two chambers by a partition wall extending in the axial direction of the mixer. One of the chambers forms a straight axial flow path for the component of the smaller volume proportion, whereas the other chamber covers the remaining cross-sectional area, which is substantially larger than the volume proportion of this component, and which is separated from the mixing chamber by a transverse wall. This other chamber thus forms a retaining volume which is filled by the component of the larger volume proportion before that component can pass a narrow passage provided in the transverse wall and reaching the mixer element. This is intended to ensure that the two different components reach the mixing chamber substantially simultaneously.
A problem exiting with this known device resides in the fact that the above-mentioned transverse wall with the narrow passage increases the flow resistance for the respective component considerably, thus rendering the overall device sluggish. As another disadvantage, the axial length of the device is significantly increased by the retaining space.
EP 0 302 819 A2 discloses a cartridge magazine for a flowable mass comprising two containers of different diameters for receiving different amounts of two components of the mass. Due to the fact that a common outlet pipe is offset from the axial center toward one edge of the cartridge system, the connecting channels between the cartridge outlets and the common outlet pipe have different lengths. In this known mixer, the above-mentioned problem of an improper mixing ratio at the beginning occurs at the second and each further application when there is no longer a time difference in time in the advancement of the components.